Microsoft and AOL Time Warner's disclosure of plans to work cooperatively on the development of secure digital content distribution struck investors as a sign that AOL's longstanding support of RealNetworks was wavering. That interpretation came despite AOL Time Warner's assertions that the Microsoft deal isn't exclusive, and that AOL will continue to work with RealNetworks.

RealNetworks' shares fell 98 cents Friday, or more than 11%, to trade at $7.79.

"We have a multiyear, multifaceted agreement with AOL, and they have assured us that this announcment with Microsoft doesn't affect that in any way," a RealNetworks spokeswoman said Friday.

Among other facets of that relationship, AOL uses RealNetworks server software for streaming audiovisual material online, and AOL has included RealNetworks' desktop software in AOL 8.0 and the preliminary AOL 9.0 package.